1) Field of the Invention
The present invention relates to a technology for registration of a position of a mobile unit in a mobile communication network.
2) Description of the Related Art
A mobile communication system is configured with a mobile unit (UE), a base-station control device (RNC), a base station (BS), a mobile switchboard (MSC), and a location register (VLR) that is provided in the mobile switchboard and in which information on a position of the mobile unit is registered. The position of the mobile unit always changes in the mobile communication system. Therefore, registration of the position of the mobile unit in advance of an incoming call is a required management for the network (mobile switchboard) to establish communication upon receiving the incoming call.
Specifically, the position is managed as a part of subscriber information in the location register by using sections locally divided called position registration areas. The same information of the position registration area is registered in the mobile unit. The registration of the position at the mobile unit is carried out by the mobile unit requesting the network when the mobile unit is powered on and when the mobile unit not during communication moves across position registration areas.
In recent years, with the increasing number of users of the mobile communication system, the amount of data on the network has been increasing accordingly. However, wireless resources between the mobile unit and the base station in the network are limited. Therefore, various methods have been studied for efficient use of such wireless resources.
In a conventional position registering method, for example, the position of the mobile unit is registered every time the mobile unit moves across position registration areas. To determine an area to which a paging signal for an incoming call is to be sent, the network always ascertains a current area in which the mobile unit is located.
FIG. 12 is a sequence diagram of a conventional position registration procedure for the mobile unit. It is assumed that three position registration areas LA1, LA2, and LA3 are present.
As shown in FIG. 12, first, (1) a mobile unit 100 is located in the position registration area LA1, and this position registration area LA1 is registered in a location register VLR in a mobile switchboard (MSC) 104 via a base station 101 and a base-station control device (RNC1) 111 (step S1200).
Next, (2) when the mobile unit 100 moves to another area, the position registration area LA2 (step S1201), the mobile unit 100 recognizes that the mobile unit 100 has entered the position registration area LA2 based on report information D1 of the current area (step S1202). Then, a position-information-registration request D2 for which a previous area, the position registration area LA1, is set is transmitted to the location register VLR via a base station (BS2) 102 and a base-station control device (RNC2) 112.
Next, (3) upon receiving the position-information-registration request D2, the mobile switchboard 104 recognizes that the mobile unit 100 is located in the position registration area LA2, and updates a latest position registration area in the location register VLR to the position registration area LA2 (step S1203). Then, the mobile switchboard 104 returns a position-information-registration request response D3 to the mobile unit 100 to notify that the latest position registration area is LA2.
Next, (4) upon receiving the position-information-registration request response D3, the mobile unit 100 recognizes completion of position registration, and then, writes and stores the position registration area LA2 in a storage area for position information in the mobile unit 100 as the latest position registration area (step S1204).
Next, (5) when the mobile unit 100 moves to the position registration area LA3 (step S1205), the mobile unit 100 recognizes, based on report information D4 of a current area, that the mobile unit 100 has entered another area, the position registration area LA3 (step S1206). Then, the position registration procedure is performed in a similar manner as a case of the position registration area LA2. First, a position-information-registration request D5 for which a previous area, the position registration area LA2, is set is transmitted to the location register VLR via a base station (BS3) 103 and a base-station control device (RNC3) 113.
Next, (6) upon receiving the position-information-registration request D5, the mobile switchboard 104 recognizes that the mobile unit 100 is located in the position registration area LA3, and then updates the latest position registration area to LA3 (step S1207). Then, the mobile switchboard 104 returns a position-information-registration request response D6 to the mobile unit 100 to notify that the latest position registration area is LA3.
Next, (7) upon receiving the position-information-registration request D6, the mobile unit 100 recognizes completion of position registration, and then, writes and stores the position registration area LA3 in the storage area as the latest position registration area (step S1208).
As described above, when the mobile unit 100 changes its location from the position registration area LA1 to the position registration area LA2, the mobile unit 100 performs the position registration procedure on the network. Thus, the position information in the mobile unit 100 and the location register VLR is updated to the position registration area LA2. In this manner, when there is an incoming call for the mobile unit 100, paging is performed with respect to the position registration area LA2. In a similar manner, when the mobile unit 100 changes its location to another area, for example, the position registration area LA3, the position information is updated to the position registration area LA3.
As described, in the conventional mobile communication, the location of the mobile unit is kept track of in a unit of position registration area that includes a plurality of base stations. Update of this position registration area is important for accurately grasping the position registration area when an incoming call is to be placed to the mobile unit in the network. Such technologies regarding the update of the position registration area are disclosed in, for example, Japanese Patent Laid-Open Publication No. H7-87554, Japanese Patent Laid-Open Publication No. H7-250365, and Japanese Patent Laid-Open Publication No. 2000-23234.
However, in the conventional technologies, the wireless resources in the network are wasted. In the conventional technologies, every time the mobile unit moves across position registration areas, a process of updating the position registration information is performed irrespectively of frequency of the incoming-call. Therefore, when the mobile unit frequently moves near a boundary of position registration areas, the process is performed very frequently because the process is performed every time the mobile unit enters one of the position registration areas. Particularly, frequent performance of such process by a mobile unit with a low incoming-call frequency leads to a wasteful use of the wireless resources, and makes it impossible for the wireless resources to be used efficiently.